Diabolik Contract
by Yeemew
Summary: Reiji Sakamaki takes an interest in Yui after she approaches him asking for help. He promises if she complies to his one simple request, he'll grant her protection from the rest of his brothers. All she has to do is play the role of a willing test subject for his drug potions…


**Reiji Sakamaki takes an interest in Yui after she approaches him asking for help. He promises if she complies to his one simple request, he'll grant her protection from the rest of his brothers. All she has to do is play the role of a willing test subject for his drug potions…**

 **Truth**

Yui paced before the heavy oak door, suppressing the fluttering sensation at the pit of her stomach as she eyed her surroundings. She couldn't tell if her shaking was attributed to her fear of the Sakamakis' incessant blood consumption, or the effects the blood consumption itself.

Her mind replayed the sharp sting of fangs piercing her skin, a barrier, she had come to realise, that offered as much protection as tissue paper did against rose thorns. Gritting her teeth, she shook the unpleasant thoughts away. _It's now or never_ , she told herself and knocked on the door.

"Who is it?" came a low, monotonous voice.

"It's Yui..." she said.

"What do you want?"

She could already sense Reiji's impatience, his voice embodied a tone which failed to hide his distaste. Yui had prepared exactly what to say.

"I'm here because I have a request..."

"Alright, if you must, come in."

Her hand hovered over the polished brass doorknob but before her fingers could grasp the handle, the door swung open, revealing a tall slender silhouette, illuminated from behind by flickering candlelight.

"Do you know what time it is, human?" Reiji eyed her with a faint air of annoyance. Yui knew it must be approaching midnight, but given the nocturnal sleep schedule in this household, she hadn't realised this would be an issue. In her panic, her meticulously planned speech evaporated from her mind.

"I... umm... I'm sorry for the disturbance... um..."

"Good grief, it would make things a great deal easier if you speak up. I was in the middle of titrating the essence of herbanacium etarancus. Sit there," he ordered, pointing to his couch. Yui obliged, at the very least, she was relieved he didn't outright turn her away. Reiji shut the door and made his way back to his desk. He picked up one of the glass pieces amidst a vast array of vials, test tubes and pipes, inspecting it with profound intensity. Yui gawked at his outlandishly complicated set up.

Reiji sighed, "You have a purpose behind your visit?"

"Um... yes. You're the only one after all this time, who hasn't taken my blood. So I feel like I can trust you most." she admitted, sheepishly.

"True. I exhibit exceptional self control in comparison to my brothers so it's not surprising that's the case." His eyes didn't stray from the dark blue liquid swivelling above the candle flame, "You haven't answered my question. What is your purpose here?"

"You see... your brothers are taking too much blood to frequently from me. If things go on at this rate, I'll lose so much blood that I won't be able to recover. Can you stop them from taking my blood?" Yui cried.

"So you came to consult me about this in the middle of the night. Did it not cross your mind that I have more pressing matters to deal with?"

"Please, you have to help me, I'm begging you!"

Reiji paused for a moment, as if weighing his options, but in reality he had already come to a decision. He'd made up his mind the moment Yui knocked. He shook the effervescing liquid, and grinned, knowing full well the dim lighting masked his expression from the girl. It was just too convenient. She had come to him willingly.

"Since I have the courtesy and an innate obligation to aid those in need, I'll make you an offer. I will protect you from my brothers, but only if you agree to certain conditions."

"Thank goodness!" Yui exclaimed, "I mean, thank you-"

"I have yet to even state my terms. Don't be so rash as to agree without consideration, human." He turned toward her, his eyes concealed by the light reflecting off his glasses. "If you comply with my orders and become a test subject for my potions, I will offer you protection from my brothers for as long as you remain in this household. I have quite a collection of samples that have yet to be tested, and of course they are... relatively safe. I want this choice to be of your own volition, so you should know that you have complete freedom to choose to accept or decline."

"Your… potions, what do they do?"

"I cannot tell you that. I have no interest in poisoning you if that's where your concern lies. I guarantee the effects are all temporary and last no longer than a few hours…"

"Okay, if I agree, you'll stop your brothers from harassing me?"

"Yes, I will not permit them to drink your blood as long as you remain in this household…" The corners of the dark haired man's mouth twitched, but he suppressed the grin, "...Unless you wish otherwise."

Yui couldn't think of anything much worse than being relentlessly pursued by five thirsty vampires. She would opt for Reiji's strange potions any day. It was undoubtedly the safer of the two. She had come to see Reiji as a fatherly figure. If there was anyone she could depend upon, it was him.

"I will require your services every day for a week. Then I will only need you on a weekly basis for follow up. If you refrain from breaking my rules and attend every session, I will also keep my word and grant you the protection you requested."

"Thank you Reiji!"

"Good. Then you must listen to my orders from now on."

He stood up before her, still holding the vial of blue liquid. Yui looked up at him quizzically from the couch.

"I will tell you to administer one potion every day, if you are to refuse even one of them, our agreement will be terminated. Do you understand?"

Yui thought this sounded rather harsh, but felt it was rather late to negotiate since she'd already eagerly accepted. "Right, so seven potions in all?"

"Indeed. I have many more I would like to test, but they will have to wait. Each drug will only remain in your system for a couple of hours."

"I see. I know you said the effects are temporary and won't harm me, but why can't you tell me what they do?"

Reiji raised his eyebrows. "The entire aim of this process is to assess the effects of a potion without preconceptions. If I were to tell you my hypotheses, your preconceptions would inadvertently cause you to demonstrate bias."

"Oh..."

"Of course in the best case scenario, we would conduct a trial, where both me, the analyst, and you, the subject, are oblivious to each drug. However, that could require a third party, and I'm hardly convinced any of my brothers would be up for the job."

Yui thought he sounded pretty knowledgable about all this, which put her at ease. He handed her the small glass filled with blue liquid. It was still warm from the flame. "I've been working on this for the past couple of days," he said proudly, "Drink it."

Yui held the unsettling liquid at a distance, hesitant to bring it closer. Seeing Reiji impatiently cross his arms, she hastily raised the vial to her lips and downed the liquid. A sweet, flowery taste lingered on her tongue. "That wasn't bad," she stated and watched with fascination as Reiji jotted down something on his leather bound notebook, something she wasn't quite able to distinguish.

"Yui, are you an honest girl?" Reiji asked abruptly.

"Umm… yes I try my best to be…" she said, confused by the random question.

"Then tell me," he said, narrowing his eyes, "Do you get a thrill out of being toyed with?"

Yui couldn't believe he would even ask such a thing. _Pfft, anyone with an ounce of self respect would reject that idea._

"I love it…" She trailed off, hearing the words leaving her mouth. They weren't the words she intended to say.

"No wait, what I meant was, I enjoy it…" Her cheeks burned. That wasn't right, she couldn't believe she was admit to something like that to Reiji. Yui closed her eyes and wished she could sink right through the ground.

When she dared to open her eyes, Reiji was not staring at her judgmentally, but working on notations in his notebook.

"That wasn't tr-" she tried to say, but the words caught in her throat. She realised, much to her horror, what Reiji had given her must be somewhat akin to a truth serum. Under Reiji's drug, she had admitted what she had been trying to deny without hesitation.

"I see," he muttered and went back to his notes. She realised he must be recording her every action. She had never felt so self-conscious.

"Yui, are you still a virgin?" He asked.

 _What was this? Reiji had no right to be prodding into matters like that_. She stared at him awkwardly unwilling to answer, her mouth a firm line. It wasn't long before she felt an incredible compulsion pushing from her gut, "No…" she blurted.

He nodded. "Very well. I suspected as much considering you felt the need to request help from me. That's all. You're free to leave my room, human."

"A-are you sure?" Yui was shocked he only asked her two questions. The interrogation was oddly exhilarating. If he had picked up on the tinge of dismay in her voice, he didn't react to it.

"Asking you questions in this environment is a fruitless ordeal. The true effects of a drug can only be observed in natural settings. I trust you will be back here in an hour to report on events."

"Wait, you mean I can leave?"

"Yes, go about your day. I want a concise oral report of events when you come back. Don't forget."

Yui excused herself. As the heavy oak door closed behind her, she glanced nervously down the dark corridor. Reiji hadn't specified for her to do anything in particular. For all he knew her _normal day_ could be hiding under her bed, avoiding all of the Sakamaki brothers like the plague. To be honest that wasn't too far from the truth. That wouldn't count as breaking any of Reiji's rules.

If she could tiptoe down the hallway past Laito's room without raising suspicions, she could easily hole up in her chambers and get through the entire hour without a single encounter. _Simple,_ she thought, and started cautiously pacing her way down the cold marble tiles. She froze at every tiny stir, like a criminal, until she finally slipped into the sanctuary of her room.

She gave a sigh of relief. This place had never seemed so welcoming. Despite this, she knew from experience it was possible one of the brothers would come looking for her. On more than one occasion, they had paid her a surprise visit, stating they felt peckish and would love a midnight snack. There was nothing she could do if they had a motive. Yui fell back onto her bed, praying she'd be lucky today.

It wasn't long before she heard footsteps. _Crap!_ Vampires didn't need to walk at human pace, they could glide and be at their desired destination at the blink of an eye. It was obviously solely to taunt her. And it was working. Yui leapt up in a frenzy and threw herself into the wardrobe, closing the door behind her just as the bedroom door swung open. She willed her heart to quieten its hammering. Someone was in her room.

"Oh, Bitch-chan~! Where have you run off to?" Laito's drawl was met with silence. All of a sudden, he smacked his fist against the wardrobe door, causing a thud to reverberate through the panels. Yui startled and hit her elbow on the back of the wardrobe.

"There's no use pretending... I can smell your sweet sweet scent," he jeered. Yui cowered behind her coats and wondered why Laito was back so soon _._ Light leaked into her hiding spot and a face she didn't want to see emerged. Yui shrank back further behind the clothes.

"Found you!" He sang as he grabbed her shoulders. "I'm tired of hide and seek, let's play another game. Hmmm... _Truth_ or dare?"

"No! I don't want to!"

"Are you sure? In that case I'll just drink your blood until you pass out again..."

"No! Wait! I'll play then."

Laito stepped into the wardrobe. "Since you seem so reluctant, I'll go first, I pick truth," he grinned a toothy grin. Yui sensed Laito knew more than he was letting on.

"What... what were you doing in the past hour?" She asked in a small voice.

"Ahh, I was going about minding my own business, but I couldn't help but overhear a little _someone_ sneak into Reiji's room. Curse my terribly good hearing," Laito laughed. "Your conversation was very interesting, who knew what you're willing to admit?"

Yui'a heart sank. So he knew. This was a disaster.

"So, truth or dare, Bitch-chan?"

"..."

"Answer me!"

"...D-dare."

"I dare you to pick truth next time."

"W-what? You can't do that-"

"Yes I can."

Yui blinked and then gasped at him in exasperation.

"Bitch-chan, ask the question!"

"T-Truth or dare?"

"Dare," Laito drawled. Maybe she could beat Laito at his own game and get out of this if she played her cards right.

"I dare you to leave my room for the next two hours."

"Oh no can do, I'll have to pass on that one."

"What?! Then I shouldn't have to pick truth," She said, her frustration bubbling to the surface, "Why do you have to be so unfair?"

"Aww little Yui is getting upset," he smirked and pushed her against the wooden back of the wardrobe. His knee pressed up against her thighs. Before she could push him away, he asked her, "So do you hate me, Bitch-chan?"

Again Yui tried to keep her mouth shut, but the overwhelming urge to speak overpowered her ability to remain silent. "Yes I hate you! How can I say I don't at this point? You treat me like I don't have any feelings, and you do it without batting an eyelid!"

"Wow, Bitch-chan, even after how good I made you feel earlier today..."

He leaned down and traced his lips in a line across her collar bone. "The more you hate me, the more I want to..." Laito's manic laughter was muffled against her skin, but it still sent shivers down her spine. He savoured the whimpers his licks evoked from the girl. Yui felt the light graze of his fangs against her neck and clenched her teeth in anticipation.

"You know contrary to what you said, I can respect your feelings. I'll ask you now, what do you want me to do?" He whispered in her ear.

"Kiss me," Yui said. Her common sense told her this was a terrible response. But Reiji's serum wouldn't allow her to lie.

"It seems you're thirstier than I am... Bitch-chan, could it be, you wanted much more from me all along?" Laito taunted. He flicked his tongue against the corner of her lips and bit down on her bottom lip. Yui flinched and tried to turn her head, but the man had entwined his fingers in her hair and was pulling her back. He tugged harder still, making her eyes water. Laito took advantage of her parted lips, slipping his tongue into her mouth. Yui let out a confused wail. She'd grown accustomed to his mouth on her skin, but she hadn't been prepared for this. Now as his tongue teased hers, it felt a lot more intimate than his previous actions.

Laito's fingers glided under her skirt, lingered on her leg and then ventured upward, toward her inner thigh. Yui grabbed his hand and struggled to refrain him from proceeding any further up.

"Oh? But we're enjoying ourselves so much. Do you really want me to stop?"

"No don't stop, I want you to touch me more..." she blurted in response to his question, completely contradicting her actions. Reiji's drug was making the situation a complete mess. She was frantically trying to push the man away and at the same time, she was begging for more. The mismatch between her words and actions delighted Laito.

"Hahaaa... seeing you struggle with your desires is fascinating," his face lit up with a devilish grin. "I have a very important question for you, Bitch-chan."

This was bad. She knew no matter what he asked, she would be unable to control the words leaving her mouth.

"Tell me your fantasies involving me. Now, what are they? Tell me!"

This was worse than bad, this was a nightmare. "I don't kn-" she choked up. She didn't want to tell him, but it was impossible to hold back, no matter how hard she tried to resist opening her mouth.

A few moments later, Laito was grinning and Yui wanted to cry. Gone was her decency. To make matters worse, the horror of a realisation struck. She would have to report the entire incident to Reiji.

"Thank you for being so honest, Bitch-chan!" Laito said gleefully.

The next thing she knew, she was sprawled on her bed, her wrists secured with an iron grip above her head. Despite being fully clothed, she felt incredibly vulnerable as Laito's gaze raked down her body, hungrily drinking in her figure. She struggled to move away, but Laito was straddling her hips. She could only clumsily squirm around.

She felt his breath against her chest as he prepared to dig into his meal.

Suddenly, the weight lifted off her body.

"Reiji..." Laito said dryly, directing his voice behind her.

Yui opened her eyes. A dark haired figure at the door was scowling at them.

"Laito," Reiji said distastefully, "that's enough, you should leave now."

"Urgh you completely ruined the mood, it's such a pity we couldn't finish this time Bitch-chan..."

"Laito, leave. You've caused enough harm already," Reiji ordered. His half-brother grinned at Yui one last time and vanished.

After Reiji carefully untied her, Yui burst into tears. He waited patiently at her bedside as she snivelled and hiccupped.

"You didn't come back at the hour mark. I assumed you'd forgotten but it turns out it was more a case of... being physically unable to do so. There's no helping it so I'll let you off this time."

He led her back to his office.

"Now, tell me all the events that occurred," he instructed, picking up his notebook and crossing his legs at his desk. The potion had yet to wear off, and much to her dismay, Yui found herself recounting the events of the past hour in profound detail.

Reiji didn't even react as she admitted her answer to Laito's perverted question. He kept writing without a pause. When he was finished, he placed his pen down on his desk and walked over to Yui.

"You may have realised this by now, but the drug I gave you was a modified truth serum," Reiji explained, "It seems to be much more potent than the average, able to coerce its user to truthfully answer questions even when they attempt to hold their silence."

Yui nodded and he continued.

"Of course, the potion will wear off within a few minutes, but before it does, I have one last question."

Yui had been asked so many humiliating questions that she'd become desensitised to it.

"Yes?" She said.

"Do you fantasise about me too?"

Yui hesitated, "No."

Reiji nodded and scribbled something down in his notebook again, face a blank slate.

Yui felt bad. "It's not that I don't like you, it's just that I can't imagine you like that…"

There was an awkward silence as they stared at each other. Yui was the first to look away, unable to bear the awkwardness.

"You are correct. You can rest assured," he picked his words carefully, "There is no way that I will act with the rash impulses comparable to that of Laito's."

Reiji cleared his throat and strolled over to the door, holding it open.

Yui walked out the room feeling the need to apologise, "Sorry…"

"I trust you'll be back tomorrow evening for the second potion," he said, and flashed a rather grim smile. Yui caught an unsettling glimpse of his protruding canines before he shut the door.


End file.
